- has taken 2 or more specific PAH medications concomitantly within 4 weeks of anticipated Visit 2 date. Only treatment naïve subjects or subjects on stable PAH-specific monotherapy with an endothelin receptor antagonist ([ERA]; bosentan, ambrisentan, or macitentan) or a prostacyclin analog ([PCA]; treprostinil, epoprostenol, or iloprost) are eligible. PAH monotherapy with one of these medications may continue without interruption during this study